Humans are social animals. They usually live in groups. They help and protect each other. They care for their children. Humans are bipedal, which means they walk on two legs. Humans have a very complex brain, which is much larger than that of the other living apes. They use language, make ideas, and feel emotions. This brain, and the fact that arms are not needed for walking, lets humans use tools. Humans use tools far more than any other species.

Humans have a long period of development after birth. Their life depends less on instinct than other animals, and more on learning. Humans are also born with their brains not so well developed as those of other mammals. This makes for an unusually long childhood, and this which makes family life important. There is a good reason for this. If their brains were better developed they would be larger, and this would make birth more difficult. In birth, the baby's head has to get through the 'birth canal', a passageway through the mother's pelvis.

Many animals use signs and sounds to communicate with each other. But humans have a complex system called language. It allows them to express ideas by using words. Humans are capable of making abstract ideas and communicating them to others. Human language can express things that are not present, or talk about events that are not happening at that time.[6] The things might be elsewhere, and the events may also have occurred at another place or time.[7] No known animals have a system of communication that is as elaborate as human language. By using words to communicate with each other, humans make complexcommunities with laws, traditions and customs. Humans like to understand the world around them. They try to explain things through myth, science and philosophy. Wanting to understand things has helped many humans make important discoveries.

Humans are part of the animal kingdom. They are mammals, which means that they give birth to their young ones, rather than laying eggs like reptiles or birds, and females feed their babies with breast milk. Humans belong to the order of primates. Apes like gorillas and orangutans are also primates. The closest living relatives of humans are the two chimpanzee species: the common chimpanzee and the bonobo. Scientists have examined the genes of humans and chimpanzees, and compared their DNA. The studies showed that 95% to 99% of the DNA of humans and chimpanzees is the same.[8][9][10][11][12]

Biologists explain the similarity between humans and other hominoids by their descent from a common ancestor. In 2001, a hominid skull was discovered in Chad. The skull is about 7 million years old, and has been classified as Sahelanthropus tchadensis. This skull may show that the date at which humans started to evolve (develop differently) from other primates is 2 million years earlier than scientists had previously thought.[13]

Long ago, there used to be other types of hominins on Earth. They were like modern humans, but not the same. Homo sapiens are the only type of hominins who are alive today.[14] The earliest known fossils of genus Homo have been called Homo habilis (handy man). The first fossils of Homo habilis were found in Tanzania. Homo hablilis is thought to have lived about 2.2 to 1.7 million years ago.[15] Another human species thought to be an ancestor of the modern human is Homo erectus.[16] There are other extinct species of Homo known today. Many of them were likely our 'cousins', as they developed differently than our ancestors.[17] A theory called the Sahara pump theory has been used to tell how different species of plants and animals moved from Africa to the Middle East, and then elsewhere. Early humans may have moved from Africa to other parts of the world in the same way.

The first truly modern humans seem to have appeared between 200,000 and 130,000 years ago.[18][19] These early humans later moved out from Africa. By about 90,000 years ago they had moved into Eurasia and the Middle East. This was the area where Neanderthals, Homo neanderthalensis, had been living for a long time (at least 350,000 years).

By about 42 to 44,000 years ago Homo sapiens had reached western Europe, including Britain.[20] In Europe and western Asia, Homo sapiens replaced the neanderthals by about 35,000 years ago. The details of this event are not known.

At roughly the same time Homo sapiens arrived in Australia. Their arrival in the Americas was much later, about 15,000 years ago.[21] All these earlier groups of modern man were hunter-gatherers.

Some modern day religions also began at this time such as Judaism and Hinduism. From the Middle Ages and beyond humanity saw an explosion of new technology and inventions. The printing press, the car, the train, and electricity are all examples of this kind of invention. As a result of the developments in technology, modern humans live in a world where everyone is connected, for example by telephone or by internet. People now control and change the environment around them in many different ways.

In early times, humans usually settled near to water and other naturalresources. In modern times if people need things they can transport them from somewhere else. So basing a settlement close to resources is no longer as important as it once was. Since 1800, the number of humans, or population, has increased by six billion.[22] Most humans (61%) live in Asia. The rest live in the Americas (14%), Africa (14%), Europe (11%), and Oceania (0.5%).

Most people live in towns and cities. This number is expected to get higher. In 2005 the United Nations said that by the end of that year, over half the world would be living in cities. This is an important change in human settlement patterns: a century earlier in 1900 only 14% of people lived in cities, in 2000 47% of the world's population lived in cities. In developed countries, like the United States, 80% of the population live in cities.[23]

Humans have a large effect on the world. Humans are at the top of the food chain and are generally not eaten by any animals. Humans have been described as super predators because of this.[24] Because of industry and other reasons humans are said to be a big cause of globalclimate change.[25]

The anatomy of female and male humans. These models had body hair and facial hair removed and head hair trimmed

Human body types can be very different from each other. The average height of an adult human is between 5 and 6 1/2 feet. The average weight is between 76 and 83 kg for males and 54–64 kg for females.[26]

Human hair grows on the underarms, the genitals, legs, arms, and on the top of the head in adults of both genders. Hair will usually grow on the ￼ face of most adult males, and on the chest and back of many adult males. In human children of both genders, long hair grows only on the top of the head. Although it might look like humans have fewer hairs than most primates, they actually do not. The average human has more hair follicles, where hair grows from, than most chimpanzees have.[27] Human hair can be brown, red, ￼￼or blond.[28] Modern humans can also have their hair in many different colors by using dye. When humans get older hair can turn grey or even white.

Human skin colors vary greatly. They can be a very pale pink all the way to dark brown. There is a reason why people in tropical areas have dark skins. The dark pigment (melanin) in the skin protects them against ultraviolet rays in sunlight. The damage caused by UV rays can and does cause skin cancer in some people. Therefore, in more sunny areas, natural selection favors darker skin color.[29][30] Sun tanning has nothing to do with this issue, because it is just a temporary process which is not inherited. In colder climates the advantage of light-colored skin is that it radiates less heat. Therefore, in less sunny areas, natural selection favors lighter skin color.[31][32][33]

Humans are not as strong as other primates of the same size. An average femaleorangutan is at least three times as strong as an average human man.[34]

The average human male needs 7 to 8 hours sleep a day. People who sleep less than this are generally not as healthy. A child needs more sleep, 9 to 10 hours on average.

The human life cycle is quite like most other mammals. The young grow inside the female mother for nine months. After this time the baby is pushed out of the woman's vagina.

Unlike most other animals, human childbirth is somewhat dangerous. Because human brains are so large, babies' heads are wide. The mothers pelvisbones are also not very wide because people walk on two legs. This combination means that sometimes either mother or baby die in childbirth.[35] The number of mothers dying in childbirth is less in the 21st century. This is because of better medication and treatment. In many poor countries the number of mothers dying is higher. Sometimes it is up to 10 times as many as richer countries.[36]

The average human baby weighs 3 – 4 kg at birth and is 50–60 cm tall. This is often less in poorer countries.[37] Many babies in poor countries often die early because of this.[38]

Life expectancy is how long you are expected to live for. This depends on many things including where you live. The highest life expectancy is for people from Monaco, 89.52 years. The lowest is for people from Chad where life expectancy is only 49.81 years.[39]

Psychology is the study of how the human mind works. The human brain is the main controller of what a person does. Everything from moving and breathing to thinking is done by the brain. The human neocortex is huge compared with other mammals, and gives us our thinking ability, and the ability to speak and understand language. Neurology is the study of how the brain works, psychology is the study of how and why people think and feel. Many aspects of life are also influenced by the hormone system, including growth and sexual development. The hormonal system (especially the pituitary gland) is partly controlled by the brain.

Art has existed almost as long as humans. People have been doing some types of art for thousands of years as the picture on the right shows. Art represents how someone feels in the form of a painting, a sculpture or a photograph.

Music has also been around for thousands of years. Music can be made with only your voice but most of the time people use instruments. Music can be made using simple instruments only such as simple drums all the way up to electric guitars, keyboards and violins. Music can be loud, fast, quiet, slow or many different styles. Music represents how the people who are playing the music feel.

Humans often categorize themselves by race or ethnicity. Human races are questionable as valid biological categories.[42] Human racial categories are based on both ancestry and visible traits such as skin color and facial features. These categories may also carry some information on non-visible biological traits, such as the risk of developing particular diseases such as sickle-cell disease.[43] Current genetic and archaeological evidence generally support a "recent single origin" of modern humans in East Africa.[44] Current genetic studies show that humans from Africa are most genetically diverse.[45] But, human gene sequences are very similar compared to many other animals.[46][47][48][49]

Ethnic groups are often linked by linguistic, cultural, ancestral, and national or regional ties. Race and ethnicity can lead to different social treatment called racism.

Religion is a belief of faith in a higher being, spirit, or any system of ideas that a group of people believe in. To have faith in a belief is to have the belief without proof that it is true. Faith can bring people together because they all believe in the same thing. Some of the things religions talk about are what happens after death, why humans exist, how humans came to exist (creation), and what is good to do and not to do (morality). Some people are very religious. Many people believe in one all-powerful god; some people believe in more than one god; some people are atheists, who do not believe in a god; and some people are agnostics, who are not sure if there is a god. People who believe in one or more gods, but do not belong to a religion, are called deists.

In the 20th century technology moved forward enough to allow a person to land on the Moon.

Technology are the things and methods which humans use to make tasks easier. Science is understanding how the universe and the things in it work. Technology used to be quite simple. It was passed on by people telling others, until writing was invented. This allowed technology to develop much quicker. Now people understand more and more about the world and the universe. The use of the telescope by Galileo, Einstein's theory of relativity, lasers, and computing are all scientific discoveries. Technology is of great importance to science, to medicine, and to everyday life.

A war is a lethal fight between large groups of people, usually countries or states. A war involves the use of lethal weapons as both sides try to kill the other. It is estimated that during the 20th century, between 167 and 188 million humans died because of war.[50] The people who fight for a state in wars are called soldiers. The people who fight in wars, but not for a state, are usually called "fighters".

Modern wars are very different from wars a thousand or even a hundred years ago. Modern war involves sabotage, terrorism, propaganda, and guerrilla warfare. In modern-day wars, civilians (people who are not soldiers) are often targets. An example of this is the nuclear bomb dropped on Hiroshima and Nagasaki at the end of World War II. The bombs killed as many as 140,000 people in Hiroshima and 80,000 in Nagasaki by the end of 1945,[51] about half on the days of the bombings. Since then, thousands more have died from wounds or illness because of exposure to radiation released by the bombs.[52] In both cities, the overwhelming majority of the dead were civilians. In Germany, Austria, and Great Britain, conventional bombs were used. About 60,595 British,[53] and 550,000 German,[54] civilians were killed by planes bombing cities.

The difference between two other animals that look like each other- rats and mice

The studies showed that, after 6.5 million years of evolution as separate species, between 95% and 99% of the DNA of humans and chimpanzees is the same. The difference between a human and a chimpanzee was about ten times greater than the difference between two unrelated humans. When this difference is compared with the difference between the DNA of mice and rats, the difference between a mouse and a rat is ten times greater than the difference between a human and a chimpanzee.

↑New York Times article Fossils in Kenya challenge linear evolution published August 9, 2007 says "Scientists who dated and analyzed the specimens — a 1.44 million-year-old Homo habilis and a 1.55 million-year-old Homo erectus — said their findings challenged the conventional view that these species evolved one after the other. Instead, they apparently lived side by side in eastern Africa for almost half a million years".

↑According to the July 2, 2007 Newsweek magazine, a woman dies in childbirth every minute, most often due to uncontrolled bleeding and infection, with the world's poorest women most vulnerable. The lifetime risk is 1 in 16 in Africa, compared to 1 in 2,800 in developed countries

60,600: John Ellis, World War II : a statistical survey (Facts on File, 1993) "killed and missing"

92,673, (incl. 30,248 merchant mariners and 60,595 killed by bombing): Encyclopaedia Britannica, 15th edition, 1992 printing. "Killed, died of wounds, or in prison .... excluding those who died of natural causes or were suicides."

92,673: Norman Davies,Europe A History (1998) same as Britannica's war dead in most cases

92,673: Michael Clodfelter Warfare and Armed Conflict: A Statistical Reference to Casualty and Other Figures, 1618–1991;

100,000: William Eckhardt, a 3-page table of his war statistics printed in World Military and Social Expenditures 1987–88 (12th ed., 1987) by Ruth Leger Sivard. "Deaths", including "massacres, political violence, and famines associated with the conflicts."

The British kept accurate records during WWII SO 60,595 was the official death toll with 30,248 for the British merchant mariners (most of whom are listed on the Tower Hill Memorial)